Wish Time
by WaiiKitsune
Summary: "It'll be nice… if I could see my beloved students graduate." Sequel to Challenge Time. Check in-fic warnings.


**Title:** Wish Time

 **Summary:** "It'll be nice… if I could see my beloved students graduate."

 **Disclaimer:** Assassination Classroom belongs to Yuusei Matsui; Katekyo Hitman Reborn! belongs to Akira Amano

 **Pairing:** None

 **Warning:** _Diverges from the AC-canonverse (for obvious reasons)_ , but also spoilers for the _**end**_ of AC. Also, a **lot** of liberty taken with in-universe facts, especially with regards to the KHR-side.

 **For Lightning515.**

 **Unbeta'd.**

* * *

 **Wish Time**

* * *

' _Gratefulness. Sorrow. Combining every emotion felt that very moment into this blade. As if to inject my soul, as if to bow in gratitude…_

 _I committed this knife… to him.'_

•••

Swallowing all his regret and pain, Nagisa Shiota brought down the knife clutched desperately in his hands. With a loud, sickening squelch, the knife penetrated the skin and sunk into the flesh beneath.

Silence followed, just for a fraction of a moment.

And then, light.

From where the knife had been plunged in, tiny bubbles of light began to emerge and in an instant, the tired and battered body transformed into countless bubbles of light. Like fireflies in the summer night, the tiny particles of light rose, glittering into the night skies. Any ordinary being passing by would have thought it to be a scene that came straight of a fairy tale, but for the ones who were there, it felt more like a funeral than anything else.

A choked sob broke the silence, and soon, more followed, until all that could be heard among the shower of light were the wrecked cries of the ones too young to loose so much.

Lost in pain and grieve and sorrow, no one noticed the figure hidden in the trees departing on shaky feet.

•••

' _Goodbye, our beloved target.'_

* * *

"Sawada Tsunayoshi, you are utterly and completely _**insane**_."

"I'm Vongola Decimo; it comes with the title. The Family doesn't help much." A roll of eyes, then a sigh. "Can you do it or not, Verde?"

The famed _Da Vinci's Reincarnation_ scoffed, despite the warnings going on in his head.

What Tsuna had requested for was not new to him; Verde had pondered over the possibilities before, and even did some primary research, deeming it _possible_ , but he had yet to conduct any actual experiments in lieu of other, more interesting researches. Making it a reality wasn't much of a problem; the topic in question is a key part of his research in the past few decades, after all. No, the key problem lies in the actual execution; it would require a power source that Verde had no access to, but Tsuna did.

And Reborn, being the protective tutor he is (even if the hitman himself vehemently denies it), would likely kill Verde over it.

"Who do you think I am?" Verde found himself answering. "Of course I can." Adjusting his glasses, he observed the Vongola Decimo sighing softly in relief, and so he asked, "I noticed that you're alone today."

"Well, I came to see _you_ , after all." Tsuna replied, smoothly side-stepping the implied query. "You know how to reach me discreetly, Verde. Contact me as soon as you have results."

Without letting the former Lightning Arcobaleno the chance to reply, Tsuna spun on his heels and walked away, ignoring the final question Verde had tossed behind him.

" _Why do you insist on saving that man?"_

* * *

It was never a question of 'why'.

And there was never an 'insist', either.

Tsuna knew, right from the start, that he was going to find a way to save him.

* * *

" _If you don't intend on marrying, Nagisa-kun could make a good heir for you."_

" _Haaaaaaahhhhh-?!_ _" If Tsuna was drinking anything, he was certain he would have choked. Wide brown eyes snapped to look at the snickering figure, his extraordinary senses already picking up the faint hint of resignation among the laughs, and Tsuna winced, putting down the document he was reading. "I'm sorry. I'm listening."_

" _Busy?"_

" _The usual paperwork. Which Reborn will attempt to murder me for when he gets back." Tsuna sighed. A moment's pause later, and the Vongola Decimo continued, "Nagisa-kun reminds me more of Takeshi, since you're on the subject."_

" _Your Rain Guardian?"_

" _Even a gentle, soothing rain can become fierce and torrential, but at the end of the day, conflicts are still settled and everything is washed away." Tsuna explained. "Nagisa-kun has a calming effect on his classmates, much like Takeshi does, even if my stubborn and prideful Guardians won't admit it."_

" _Just the other day, the class had an all-out conflict. Over lil' ol' me! Oh, I feel so special~"_

" _Speaking of which… we're rapidly approaching it, aren't we?" Tsuna murmured. "…The deadline."_

" _Ahh yes. March is coming soon. Graduation time."_

 _A brief silence passed, and then, "Do you… have any regrets, Koro-sensei?"_

" _I'd like to think my life is fine the way it is. Unconventional, of course, but I am pleased with how it turned out. So, no, I don't believe I have any regrets."_

"… _I sense a 'but' in there." Tsuna prodded._

" _Nothing slips past the famous Vongola Hyper Intuition it seems. Well. I do not currently regret anything, but perhaps, in the near future, I might possibly regret one thing."_

" _What… would that be, if you don't mind me asking?"_

" _I suppose, if anything… It'll be nice… if I could see my beloved students graduate."_

* * *

' _In hindsight,'_ Tsuna thought, calmly meeting the depthless black eyes currently attempting to burn a hole through his head, _'my plan has been going on_ too _smoothly.'_

"It seems like we've been caught." Verde spoke, a background of glittering lights floating into the sky shadowing his face.

(Tsuna patiently resisted the urge to retort, rather childishly, "Really? What tipped you off, genius?")

"Tsuna. Explain. _Now._ "

Against his (possibly) better judgment, the brunet decided to keep his silence. Verde had long since turned back to the sight behind them, continuing his data collection of the scenario, all but leaving the Vongola Decimo to deal with the impending disaster.

A second call of his name, this time much sharper and forceful, but Tsuna made himself ignore it momentarily in a bid for time. In the two years he spent following Timoteo around, learning from the previous Don Vongola, as well as the two years after he officially took over, Tsuna had learnt many, many things about confrontations; that not all confrontations require an immediate response was one of those things. That said, Tsuna knew that in the current situation, it would do him more good to respond, yet at the same time, Tsuna also knew that not only did he had no defence for his actions, he also only had this one chance to make his plan work, for his furious tutor would never allow him another opportunity.

And so could, he only pray that Verde could finish his research before the hitman inevitably stepped in and dragged them back.

Surprisingly, however, Reborn did not interfere.

It meant that his tutor, however enraged, was willing to give his student a chance. (That, and that the hitman had every confidence in stopping Tsuna's plans.)

* * *

Using what seemed to be all of his ancestral blessings, Tsuna had managed to send Verde back, leaving him in his office, alone with the most dangerous man in the world.

"What are you—"

"—I'm not trying to save Cel, Reborn." Tsuna injected, his voice quiet but firm. "Not in the way you think."

The scepticism was clear in Reborn's eyes, but nonetheless, the hitman gestured for Tsuna to continue. With determination set in every fibre of his body, Tsuna took a deep breath, looked directly into his tutor's eyes, and continued.

"It would be so easy to save him… The world government may detest us, but they cannot deny the existence and influence of the underworld. Even if I act independent of Vongola, the power I hold still makes it simple enough to pressurise the government to back off, but I can't. I would be erasing the meaning of his death; I can't do that. Not back then, as I watched the world government put into place their final plans against Cel, not when I watched Cel defend his students with all of his life and strength, not even when I watched as Class 3-E completed the assassination of their teacher… and certainly not now, two months after the fact."

"I can't let Cel's death go just like this. I have accepted his death as a necessity, but before I fully let this go, there is something that I must… no, that I wish to do: fulfil Cel's wish. It is the only regret he has, and is the greatest wish any teacher could possibly have."

"Please, Reborn. Let me be selfish. I want to grant Cel's wish. Please, let me."

The hitman, silent all this time, didn't even need to ask Tsuna to clarify. Most of what the brunet said, Reborn has already known, or guessed. The only thing he couldn't figure out was Tsuna's motivations, and now, having heard them, he was almost inclined to give in to his student's request—keyword being, _'almost'_.

"The price of _your_ wish… is your life."

"Not quite." Tsuna twitched in a smile Reborn hated the most—the Vongola Decimo 'perfectly-polite-public' smile. "Rather than my life, the price is my time. A better use of my time, I'd say. Mafia Dons don't exactly have a long life expectancy, after all."

"And it's _our_ job to make sure you live as long as Timoteo, who, as we both know, constantly likes to remind Coyote that he's still _'alive and young'_ while holding his aching back." Reborn retorted, barely holding back a roll of his eyes. With deliberate silence, the hitman retrieved the gun cleaning kit he had stashed in the Don Vongola office years ago and began cleaning his gun methodically. "You can't guarantee this will go the way you want it to. Not even with Hyper Intuition."

"You believe Cel will betray me?"

"He is… was… an assassin. The strongest in the world, no less." Reborn stated.

"And you're a hitman. The strongest in the world as well. And I trust you with my life." Tsuna replied matter-of-factly. An amused smile lit his face as the Vongola Decimo continued, "Are you implying that I shouldn't be trusting you, Reborn?"

"You should always hold some caution." Reborn replied amusedly.

"Oh, don't worry; I'm well-trained in the art of dodging bullets." Tsuna tossed back. The atmosphere created by the banter did not last long, and the smile faded from both of their faces. Glancing down at the small lion cub sleeping soundly on his desk, Tsuna let his bangs shadow his eyes as he continued, "My time is also the leash. Just as I can grant it, I can take it back easily. That said…" He looked up, eyes meeting Reborn's directly. And, smiling fondly, "I trust that Cel won't betray my trust in him."

And with that, Reborn knew he had lost.

Sighing in mock irritation, the hitman bit out, "You're going to do it whether I agreed to it or not. Better for me to agree and keep an eye on you, than to let you go behind my back."

"It's true that I would have gone through with it no matter what you say," Tsuna agreed. "But I'd rather you agree to it than for me to go behind your back."

 _(…Definitely lost.)_

* * *

The city hall reserved by Kunugigaoka Junior High School was completely filled with students, parents, teachers and selected guests.

As Karasuma had promised, Class 3-E sat at the front alongside all the graduating classes. Be it because of the class's performance throughout the year having convinced the school, or be it because the school was currently in public, there was not a single jeer to be heard nor a sneer to be found. The hall's atmosphere was simply filled with pride as all Third Years of Kunugigaoka Junior High School took to the stage, one-by-one, to receive their certificate of graduation.

' _It's surreal'_ , Nagisa had thought as he approached the stage. _'A year ago, if someone told us we'd be graduating with the rest of the school, we'd have laughed and called them delusional. Yet, now, here we are. I'm about to receive my graduation certification from Chairman Asano. This is all thanks to… Koro-sensei…'_

"I like the look in your eyes today." Gakuhou spoke, smiling sincerely in a way Nagisa had never seen before. "It must be the result of your teacher's instructions. Congratulations on graduating."

"Thank you," Nagisa smiled. "Please stay well… but don't go overboard." He added, almost cheekily, before stepping off the stage.

As he walked, Nagisa's eyes instinctively flickered across the hall, trying to take in the sight that he would never see again. He looked at the massive hall (nothing lesser for the prestigious Kunugigaoka Junior High, after all), Class 3-E proudly occupying their seats in the hall; the faint, barely visible smile on Karasuma's face (a contrast to Irina's wider, brighter one), and the sea of parents (who were terribly at hiding the prejudice in their eyes). When his eyes reached the back of the darkened hall, Nagisa nearly stumbled on the stairs he was taking.

' _Huh? Is that…'_

* * *

Class 3-E found themselves surprised for the second time that day when the graduation ceremony dispersed and, as Karasuma had warned them beforehand, they were nearly swamped by the media reporters wanting the dirt on what happened on the mountain mere hours ago. The class was fully prepared to ignore them and move through, however hard it would be, but they were pleasantly surprised when the other students, led by the Five Virtuosos, boldly stepped forth to block the reporters and escorted them to the parking lot, where a bus Karasuma arranged for beforehand awaited. When they had safely gotten on, the bus took them back to the mountain campus, where the final debriefing would take place.

"T-Tsuna-san?"

"Congratulations on your graduation!" Tsuna smiled, waving a greeting as the class exited the bus. "It has been a long year, but you've all made it. And…" He let his smile turned bitter. "I've heard about what happened to Koro-sensei from Karasuma-san. I'm sorry for your loss."

The reminder of their loss, however polite, was enough to overcome the joy of their graduation, especially out in the mountains where there were little people to see their sorrow.

"T-Tsuna-san," Nagisa called, already attempting to lift the gloomy atmosphere. "Who's the child on your shoulder?"

"Oh, him?" Tsuna glanced at the small, cursed-Arcobaleno-sized child sitting on his shoulder. "His name is Renato. I'm looking after him temporarily, so I brought him along. And you've already met Reborn. I had to bring that one along because he's very grumpy." (He cheerfully ignored the murderous look on the hitman's face.)

As the class politely greeted the quiet, smiling child, they couldn't help but feel a sense of nostalgia, as though they had seen the black-haired, black-eyed child from somewhere far away, even though there was no way they'd meet an Italian (maybe?) child before.

"Tsuna," Reborn called out, breaking them out of their reveries. "It's time to go."

"A-Already?" Isogai said, several of the other students echoing his sentiments. "Wait, Tsuna-san why are you sulking too—"

"Because Reborn is mean." Tsuna sighed dramatically. "Well, I shan't hold you up any longer. At this rate, Karasuma-san is going to glare a hole through my brain." As Reborn began walking out, Tsuna glanced at the students of Class 3-E standing before him, and he smiled. "Once again, congratulations of your graduation. You are all his pride; of that, I'm sure."

* * *

"Tsunayoshi-kun… Thank you."

"This is… the only thing I can do for you. I'm sorry I couldn't do anything more."

"Any more you do would be going against the laws of nature. This is enough. I am… content."

"Koro-sensei…"

"Now, I shouldn't encroach on your lifespan any longer. You should return to your own time as soon as possible as well."

"…Farewell, Koro-sensei. It has been an honour to know you."

* * *

" _Congratulations on graduation, my beloved students. The time of parting has come. Being able to teach you for the past year has been the greatest joy for me. Walk on, my students, with your head held up. You have earned it for yourselves. Goodbye."_

* * *

A/N: It's been four years since I've met Lightning515! Time really flies~ Here's to more years of friendship and pai— I mean, joy! (*cough*)

Thank for reading! Ciao Ciao~


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